Monitoring Global Tropospheric OH Concentrations using Satellite Observations of Atmospheric Methane

Zhang, Yuzhong; Jacob, Daniel J.; Maasakkers, Joannes D.; Sulprizio, Melissa P.; Sheng, Jianxiong; Gautam, Rahul; Worden, J.

doi:10.5194/acp-2018-467

Cited by 7 publications

(22 citation statements)

References 37 publications

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“…Additional constraints on the CH 4 loss rate may also permit a more robust estimate of emissions patterns (5) and assist efforts to assess model O 3 and CH 4 budgets (51). This work is complementary to continuing research into budget-based global OH constraints (23,24). Such methods are inherently subject to uncertainties in emissions and transport; in contrast, our method hinges on our understanding of atmospheric composition and chemistry.…”

Section: Conclusion and Next Stepsmentioning

confidence: 95%

“…Although powerful, MCF-derived OH constraints are also inherently limited in several respects. Declining MCF concentrations presage reduced precision for inferred OH in the coming decade, leading the community to seek alternatives (21)(22)(23)(24). All budget/inversion methods convolute source and sink anomalies, and uncertainties in emissions are not always well known (22).…”

Section: Significancementioning

confidence: 99%

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Mapping hydroxyl variability throughout the global remote troposphere via synthesis of airborne and satellite formaldehyde observations

Wolfe

Nicely

Clair

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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The hydroxyl radical (OH) fuels tropospheric ozone production and governs the lifetime of methane and many other gases. Existing methods to quantify global OH are limited to annual and global-to-hemispheric averages. Finer resolution is essential for isolating model deficiencies and building process-level understanding. In situ observations from the Atmospheric Tomography (ATom) mission demonstrate that remote tropospheric OH is tightly coupled to the production and loss of formaldehyde (HCHO), a major hydrocarbon oxidation product. Synthesis of this relationship with satellite-based HCHO retrievals and model-derived HCHO loss frequencies yields a map of total-column OH abundance throughout the remote troposphere (up to 70% of tropospheric mass) over the first two ATom missions (August 2016 and February 2017). This dataset offers unique insights on near-global oxidizing capacity. OH exhibits significant seasonality within individual hemispheres, but the domain mean concentration is nearly identical for both seasons (1.03 ± 0.25 × 106 cm−3), and the biseasonal average North/South Hemisphere ratio is 0.89 ± 0.06, consistent with a balance of OH sources and sinks across the remote troposphere. Regional phenomena are also highlighted, such as a 10-fold OH depression in the Tropical West Pacific and enhancements in the East Pacific and South Atlantic. This method is complementary to budget-based global OH constraints and can help elucidate the spatial and temporal variability of OH production and methane loss.

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Section: Conclusion and Next Stepsmentioning

confidence: 95%

Section: Significancementioning

confidence: 99%

Mapping hydroxyl variability throughout the global remote troposphere via synthesis of airborne and satellite formaldehyde observations

Wolfe

Nicely

Clair

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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“…The distribution of the methane loss rate due to Cl atoms is shown in Figure 8. The general latitudinal and seasonal patterns are not sufficiently different from OH (shown in Zhang et al, 2018) to allow any effective separation between the two.…”

Section: Atom and Its Impact On Vocsmentioning

confidence: 82%

“…This is a small effect considering the 10% current uncertainty in the overall atmospheric lifetime of methane (Prather et al, 2012). Zhang et al (2018) suggested that satellite observations of the global distribution of atmospheric methane could be used to independently constrain methane sources and the dominant sink from oxidation by tropospheric OH. The distribution of the methane loss rate due to Cl atoms is shown in Figure 8.…”

Section: Atom and Its Impact On Vocsmentioning

confidence: 99%

The role of chlorine in tropospheric chemistry

Wang¹,

Jacob²,

Eastham³

et al. 2018

Preprint

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Abstract. We present a comprehensive simulation of tropospheric chlorine within the GEOS-Chem global 3-D model of oxidant-aerosol-halogen atmospheric chemistry. The simulation includes explicit accounting of chloride mobilization from sea-salt aerosol by acid displacement of HCl and by other heterogeneous processes. Additional sources of tropospheric chlorine (combustion, organochlorines, transport from stratosphere) are small in comparison. Reactive gas-phase chlorine Cl*, including Cl, ClO, Cl2, BrCl, ICl, HOCl, ClNO3, ClNO2, and minor species, is produced by the HCl + OH reaction and by heterogeneous conversion of sea-salt aerosol chloride to BrCl, ClNO2, Cl2, and ICl. The model simulates successfully the observed mixing ratios of HCl in marine air (highest at northern mid-latitudes) and the associated HNO3 decrease from acid displacement. It captures the high ClNO2 mixing ratios observed in continental surface air at night with chlorine of sea salt origin transported inland as HCl and fine aerosol. It simulates successfully the vertical profiles of HCl measured from aircraft, where enhancements in the continental boundary layer can again be explained by transport inland of the marine source. It does not reproduce the boundary layer Cl2 mixing ratios measured in the WINTER aircraft campaign (1&#8211;5&#8201;ppt in the daytime, low at night); the model is too high at night compared to WINTER observations, which could be due to uncertainty in the rate of the ClNO2 + Cl&#8722; reaction, but we have no explanation for the daytime observations. The global mean tropospheric concentration of Cl atoms in the model is 620&#8201;cm&#8722;3 and contributes 1.0&#8201;% of the global oxidation of methane, 20&#8201;% of ethane, 14&#8201;% of propane, and 4&#8201;% of methanol. Chlorine chemistry increases global mean tropospheric BrO by 85&#8201;%, mainly through the HOBr + Cl&#8722; reaction, and decreases global burdens of tropospheric ozone by 7&#8201;% and OH by 3&#8201;% through the associated bromine radical chemistry. ClNO2 chemistry drives increases in ozone of up to 8&#8201;ppb over polluted continents in winter.

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“…Furthermore, model representations of stratosphere‐troposphere exchange will require improvement, to ensure accurate transport from the upper atmosphere, where 14 CO is produced, to surface observation sites. (iii) CH 4 data themselves can potentially be used to infer [OH] in addition to other terms in the global CH 4 budget, provided that there is high enough spatial density and global coverage in the measurements (Maasakkers et al, ; Y. Zhang et al, ). Such an approach relies on the fact that, compared to observations of lower abundance compounds such as MCF, dense observations of CH 4 are possible from space.…”

Section: Top‐down Source and Sink Estimation At Global And Regional Smentioning

confidence: 99%

Advancing Scientific Understanding of the Global Methane Budget in Support of the Paris Agreement

Ganesan

Schwietzke²,

Poulter

et al. 2019

Global Biogeochemical Cycles

100

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The 2015 Paris Agreement of the United Nations Framework Convention on Climate Change aims to keep global average temperature increases well below 2 °C of preindustrial levels in the Year 2100. Vital to its success is achieving a decrease in the abundance of atmospheric methane (CH4), the second most important anthropogenic greenhouse gas. If this reduction is to be achieved, individual nations must make and meet reduction goals in their nationally determined contributions, with regular and independently verifiable global stock taking. Targets for the Paris Agreement have been set, and now the capability must follow to determine whether CH4 reductions are actually occurring. At present, however, there are significant limitations in the ability of scientists to quantify CH4 emissions accurately at global and national scales and to diagnose what mechanisms have altered trends in atmospheric mole fractions in the past decades. For example, in 2007, mole fractions suddenly started rising globally after a decade of almost no growth. More than a decade later, scientists are still debating the mechanisms behind this increase. This study reviews the main approaches and limitations in our current capability to diagnose the drivers of changes in atmospheric CH4 and, crucially, proposes ways to improve this capability in the coming decade. Recommendations include the following: (i) improvements to process‐based models of the main sectors of CH4 emissions—proposed developments call for the expansion of tropical wetland flux measurements, bridging remote sensing products for improved measurement of wetland area and dynamics, expanding measurements of fossil fuel emissions at the facility and regional levels, expanding country‐specific data on the composition of waste sent to landfill and the types of wastewater treatment systems implemented, characterizing and representing temporal profiles of crop growing seasons, implementing parameters related to ruminant emissions such as animal feed, and improving the detection of small fires associated with agriculture and deforestation; (ii) improvements to measurements of CH4 mole fraction and its isotopic variations—developments include greater vertical profiling at background sites, expanding networks of dense urban measurements with a greater focus on relatively poor countries, improving the precision of isotopic ratio measurements of 13CH4, CH3D, 14CH4, and clumped isotopes, creating isotopic reference materials for international‐scale development, and expanding spatial and temporal characterization of isotopic source signatures; and (iii) improvements to inverse modeling systems to derive emissions from atmospheric measurements—advances are proposed in the areas of hydroxyl radical quantification, in systematic uncertainty quantification through validation of chemical transport models, in the use of source tracers for estimating sector‐level emissions, and in the development of time and space resolved national inventories. These and other recommendations are proposed for...

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Monitoring Global Tropospheric OH Concentrations using Satellite Observations of Atmospheric Methane

Cited by 7 publications

References 37 publications

Mapping hydroxyl variability throughout the global remote troposphere via synthesis of airborne and satellite formaldehyde observations

Mapping hydroxyl variability throughout the global remote troposphere via synthesis of airborne and satellite formaldehyde observations

The role of chlorine in tropospheric chemistry

Advancing Scientific Understanding of the Global Methane Budget in Support of the Paris Agreement

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